This invention relates to transparent articles used for windows and the like, and more particularly, to such articles that have metallic mesh embedded therein.
It is a common practice to place a grid of fine electrical conductors on or inside a transparent article. Depending upon the arrangement and dimensioning of the electrical conductors and the wavelength of the radiation impinging radiation, the grid can either permit the transmission of radiation through the transparent article or block its transmission. The grid, formed of a plurality of intersecting metallic stripes, is connected at the periphery of the article to an electrical ground or to a voltage source.
The grid can serve any of a variety of functions. An electrical current can be transmitted through the grid to heat the metallic stripes and thence the transparent article to accomplish de-icing, for example. In another application, the grid is electrically grounded and serves to block the intrusion of electromagnetic interference (EMI) into the interior of the structure in which the window is set, while permitting the transmission of light through the window.
The transparent article with its embedded grid and associated connections can be prepared by any of several approaches. In one, a pattern of thin conductive metallic stripes is deposited upon a transparent substrate. A second piece of the substrate material is placed over the first piece and pressed against the first piece, with the pattern of metallic stripes sandwiched between the two transparent pieces. In another approach, the pattern of thin conductive stripes is deposited upon a transparent substrate. A top layer is deposited overlying the pattern by vapor deposition or other technique.
The inventors have recognized that these techniques, while operable for some applications, have drawbacks when they are used in an attempt to prepare transparent windows (including flat windows and curved domes) of extremely high optical quality. In the approach where the grid is sandwiched between two solid pieces, the resulting stresses in the window diffract and thence distort the transmitted radiation. In the approach where the top layer is vapor deposited, the production of the required thin films can be difficult. Masking of the substrate is not readily accomplished, particularly at the periphery of the substrate so that external bus connections to the grid can be made. In both approaches, it is difficult to disassemble the window to gain access to the grid, in the event that repairs to the grid are necessary, for example.
There is a need for an improved approach to the incorporation of metallic grids into transparent structures. This approach should produce an optically high-quality window, while also permitting disassembly of the window for access to the grid in some cases. The present invention fulfills this need, and further provides related advantages.